Aqueous process for making a stable fluoropolymer dispersion

ABSTRACT

A novel aqueous polymerization process for making fluoropolymer dispersions is disclosed in which non-ionic non-fluorinated emulsifier is used to produce fluoropolymer emulsions. The emulsifiers used in the invention are those that contain segments of polyethylene glycol, polypropylene glycol, and/or polytetamethylene glycol with repeating units of 3 to 100. The process and fluoropolymer produced contain no fluorinated surfactant.

This application is a continuation-in-part of U.S. application Ser. No.11/149,797, filed Jun. 10, 2005, abandoned.

FIELD OF THE INVENTION

The invention relates to a process for making fluoropolymer dispersionsusing non-fluorinated, non-ionic emulsifiers. The emulsifiers containsegments of polyethylene glycol, polypropylene glycol and/orpolytetramethylene glycol.

BACKGROUND OF THE INVENTION

Fluoropolymers are generally made by an aqueous dispersion process,which provides a suitable heat sink for controlling the heat ofpolymerization and can produce a high yield and high molecular weightrelative to polymerization conducted in an organic solvent. In order toachieve stable dispersion or emulsion, a suitable surfactant oremulsifier must be employed. Fluorinated-surfactants are generally usedbecause they can yield stable particle and high molecular weightfluoropolymers. However, the fluorinated-surfactants typically used inemulsion polymerization of fluoropolymers, such as the ammonium salt ofperfluoro octanoic acid or salts of perfluoro alkyl sulfonic acids areexpensive. They also present an environmental concern related tobio-persistence.

It is therefore desirable to carry out an aqueous dispersionpolymerization of fluoropolymers in the absence offluorinated-surfactants, without compromising the properties of theresultant fluoropolymers. It would also be desirable to produce smallparticle size emulsion so that latex stability during storage as well asquality of film formation is improved. Furthermore, it would bedesirable to produce a dispersion and/or fluoropolymer resin havingfewer extractable ions and extractable low molecular weight polymers,while generally yielding fluoropolymers that have similar or evenimproved properties compared to analogous fluoropolymers made inpresence of added fluorinated-surfactants.

An aqueous dispersion polymerization is used as a means to control thethermal and viscosity problems associated with producing fluoropolymers.An aqueous dispersion consists of a discontinuous fluoropolymer phasedispersed throughout a water phase. Examples of aqueous dispersionpolymerization include but not limited to emulsion and suspensionpolymerizations.

Emulsion polymerization of vinylidene fluoride (VF₂) at moderatepressures and temperatures using fluorinated surfactants, free radicalinitiators, and trichlorofluoromethane as chain transfer agent is taughtin the U.S. Pat. No. 4,569,978 in which (VF₂) based polymers areproduced with reduced tendency to generate cavity and greater resistanceto discoloration at elevated temperatures. The process was refined inthe U.S. Pat. No. 6,794,264 wherein particularly ozone depleting agent(trichlorofluoromethane) was replace by propane which is environmentallyfriendly chemical. It is noteworthy that in both processes fluorinatedsurfactant was needed to produce stable emulsion. For example,perfluorocarboxylate salts was used to stabilize fluoropolymer emulsionpolymerizations, with the most common example being ammoniumperfluorooctanoate or ammonium perfluoronanoate. The high degree offluorination is thought to be necessary to prevent chain transferreaction between a growing polymer chain and the surfactant which inturn may result in lowering molecular weight and/or inhibition of thepolymerization.

Many attempts have been made to find a suitable emulsifier in place offluorinated surfactant for such polymerizations, as disclosed in thebackground section of U.S. Pat. No. 6,512,063 in which sodium salt ofhydrocarbon sulfonates as non-fluorinated but ionic emulsifier wasemployed. The ionic emulsifiers are undesired for high purityapplications due to high levels extractable ions. Furthermore, alkylsulfonates act as implicit chain transfer agent in the emulsionpolymerization of fluoropolymers, as a result, it cannot be used insufficient amount to produce small particle size latex withoutinhibiting such polymerizations.

Emulsifier-free aqueous emulsion polymerization process for makingfluoropolymer such as TFE and/or VDF copolymers is described in WO02/088207. In emulsifier free emulsion polymerization, first onlyinorganic ionic initiators such as persulfates or permangamates may workwhereas organic peroxide initiators would not work. Second, the particlesize of emulsifier free emulsion of fluoropolymers would be large; as aresult, the shelf-life of latex would be very limited. Third, the solidcontent of emulsifier free latex is limited to low or moderate solids,where in fact a high solid latex is desirable in variety of commercialapplications.

U.S. pat. Appl. No. 2006/0135716 describes fluoroelastomers having a Tgbelow −10° C. by copolymerizing perfluoropolyethers using an emulsionprocess. Alkyl groups on the listed surfactants exhibit high chaintransfer activities in a conventional fluoropolymer emulsion when usedat a sufficient amount to produce a stable latex, and as a result, themolecular weight of the resultant polymer will be considerably reduced.Thus, the properties of fluoroelastomers described in this reference aresignificantly different from fluoropolymers contemplated by the presentinvention.

The U.S. Pat. No. 6,794,550 describes a process in which fluoropolymerdispersions were synthesized in the presence of fluorinated emulsifiers.Nonionic emulsifiers were post-added to the dispersions, then a portionof fluorinated surfactant was removed by means of steam-volatilizationat low pH. The disclosed process could never remove all of thefluorinated surfactant; therefore, the resultant fluoropolymerdispersion is not absolutely free of fluorinated surfactant, and aportion of the fluorinated surfactant will remain in the finaldispersion. Moreover, the shelf-stability of said dispersion would beconsiderably reduced if not totally diminished due to heating thedispersion up to the steaming point at low pH. Further, the use offluorosurfactants in the process, even when latter removed creates awaste stream containing fluorosurfactants and the associatedenvironmental issues.

A method has been disclosed in WO 2005/082785 for removing fluorinatedsurfactant form waste water stream. The method comprises (i) adding anon-fluorinated surfactant to the waste water (ii) contacting the wastewater with adsorbent particles to adsorb a portion of the fluorinatedsurfactant onto the particles (iii) separating the waste water andadsorbent particle. Although using fluoropolymer dispersion instead ofwaste water is not contemplated by inventors but can be practiced withsome difficulties. The resultant fluoropolymer dispersion; however, isnot absolutely free of fluorinated surfactant. A portion of fluorinatedsurfactant used in the first step of process will remain in the finaldispersion.

“Fluorinated surfactant” and “fluoro-surfactant” as used herein meansthat the main surfactant chain contains fluorine atoms whereas in thepresent invention “non-fluorinated surfactant” means that there is nofluorine on the main chain but the terminal groups can contain fluorineatoms.

Surprisingly it has now been found that a stable fluoropolymerdispersion can be made by a process using absolutely no fluorinatedsurfactant and using only non-fluorinated, non-ionic emulsifierscontaining segments of polyethylene glycol polypropylene glycol, and/orpolytetramethylene glycol having varieties of different terminal groupsand functions. The fluoropolymer dispersions produced have good latexstability and shelf-life, and are coagulum and adhesion free. Thesedispersions are absolutely free of fluorinated or partially fluorinatedsurfactant. In other words, no fluorinated surfactant is ever used tosynthesize, produce, and/or post stabilize in this present invention.

SUMMARY OF THE INVENTION

The invention relates to a stable aqueous fluoropolymer dispersion freeof fluoro-surfactant comprising:

-   -   a) a fluoropolymer containing at least 50 mole percent of        fluoromonomer units; and    -   b) from 100 ppm to 2 percent, based on the weight of the        fluoropolymer solids, of one or more emulsifier(s) having        polyethylene glycol, polypropylene glycol and/or        polytetramethylene glycol (PTMG) segments with repeating units        of from 2 to 100        wherein the fluoropolymer is in the form of particles having a        particle size from 50 to 500 nm and wherein said fluoropolymer        dispersion has a solid content of 15 to 70 weight percent.

The invention also relates to a process for making a stable aqueousfluoropolymer dispersion by polymerizing at least one fluoromonomer inan aqueous medium comprising at least one emulsifier consisting of anon-fluorinated, non-ionic emulsifier containing polyethylene glycolpolypropylene glycol, and/or polytetramethylene glycol segments withrepeating units between 2 to 200, wherein no fluorosurfactant is used inthe process.

DETAILED DESCRIPTION OF THE INVENTION

The term “fluoromonomer” as used according to the invention means afluorinated and olefinically unsaturated monomer capable of undergoingfree radical polymerization reaction. Suitable exemplary fluoromonomersfor use according to the invention include, but are not limited to,vinylidene fluoride, vinyl fluoride; trifluoroethylene,tetrafluoroethylene (TFE), chlorothrifluoroethylene (CTFE) andhexafluoropropylene (HFP) and their respected copolymers. The term“fluoropolymer” refers to polymers and copolymers (including polymershaving two or more different monomers, including for exampleterpolymers) containing at least 50 mole percent of fluoromonomer units.

The term “vinylidene fluoride polymer” used herein includes bothnormally high molecular weight homopolymers and copolymers within itsmeaning. Such copolymers include those containing at least 50 molepercent of vinylidene fluoride copolymerized with at least one comonomerselected from the group consisting of tetrafluoroethylene,trifluoroethylene, chlorotrifluoroethylene, hexafluoropropene, vinylfluoride, pentafluoropropene, perfluoromethyl vinyl ether,perfluoropropyl vinyl ether and any other monomer that would readilycopolymerize with vinylidene fluoride. Particularly preferred arecopolymers composed of from at least about 70 and up to 99 mole percentvinylidene fluoride, and correspondingly from 1 to 30 percenttetrafluoroethylene, such as disclosed in British Patent No. 827,308;and about 70 to 99 percent vinylidene fluoride and 1 to 30 percenthexafluoropropene (see for example U.S. Pat. No. 3,178,399); and about70 to 99 mole percent vinylidene fluoride and 1 to 30 mole percenttrifluoroethylene. Terpolymers of vinylidene fluoride, hexafluoropropeneand tetrafluoroethylene such as described in U.S. Pat. No. 2,968,649 andterpolymers of vinylidene fluoride, trifluoroethylene andtetrafluoroethylene are also representatives of the class of vinylidenefluoride copolymers which can be prepared by the process embodiedherein.

As discussed in the prior art section, the field of VDF based copolymersis rich with teachings on how to produce copolymer resins with differentmechanical properties in presence of fluoro-surfactant. It is thereforeimportant to understand the background of the present invention in thecontext of the teaching how to produce VDF based polymers which areclassed as thermoplastic, elastomer-modified thermoplastic, orelastomeric resins without using any fluorinated surfactant.

Emulsifiers suitable for use in this invention are non-fluorinatednon-ionic emulsifiers containing segments of polyethylene glycol (PEG),polypropylene glycol (PPG), polytetramethylene glycol (PTMG) or acombination thereof, with repeating units between 2 to 200, preferablybetween 3 to 100, and more preferably 5 to 50. The glycol-basedemulsifiers used in this invention include, but are not limited to,polyethylene glycol acrylate (PEGA), polyethylene glycol methacrylate(PEG-MA), dimethyl polyethylene glycol (DMPEG), polyethylene glycolbutyl ether (PEGBE), polyethylene glycol (PEG), polyethylene glycolphenol oxide (Triton X-100), polypropylene glycol acrylate (PPGA),polypropylene glycol (PPG) polypropylene glycol acrylate (PPGA),polypropylene glycol methacrylate (PPG-MA), and polytetramethyleneglycol (PTMG)

The emulsifier may contain the same or different terminal groups on eachend, such as hydroxyl, carboxylate, benzoate, sulfonic, phosphonic,acrylate, methacrylate, ether, hydrocarbon, phenol, functionalizedphenol, ester, fatty ester, and the like. The terminal group can containhalogen atoms like F, Cl, Br and I, and also other groups or functionssuch as amine, amid, cycle hydrocarbon, and others. For example,polyethylene glycol acrylate with Mn about 375, polyethylene glycol withMn about 570, polyethylene glycol methacrylate with Mn about 526,dimethyl polyethylene glycol with Mn about 250, polyethylene glycolbutyl ether with Mn about 206, polyethylene glycol with Mn about 300,polypropylene glycol acrylate with Mn about 475, polypropylene glycolwith Mn about 400, polypropylene glycol methacrylate (PPG-MA) with Mnabout 375, and polytetramethylene glycol with Mn about 250 andpolyethylene glycol with phenol oxide end group and many other examplecan be used in this invention to produce stable fluoropolymerdispersion.

The chemical structure of the emulsifier of this invention could bealtered so that PEG, PPG and/or polytetramethylene glycol (PTMG). wouldnot be the main backbone but the essential properties such as watersolubility, chain transfer activities, and protective behaviors remainsthe same.

The emulsifier is used at a level of from 100 ppm to 2 percent, 100 ppmto 1 percent and 100 ppm to ½ percent, based on the total polymer solidsof the fluoropolymer formed in the dispersion.

In the polymerization process, the emulsifier of this invention could beadded all upfront prior to polymerization, fed continuously during thepolymerization, fed partly before and then during polymerization, or fedafter polymerization started and progressed for a while.

The dispersion of the invention has a solids level of from 15 to 70weight percent, preferably from 20 to 65 weight percent. Thefluoropolymer particles in the dispersion have a particle size in therange of 50 to 500 nm, and preferably from 100-350 nm.

The manner of practicing the invention will now be generally describedwith respect to a specific embodiment thereof, namely polyvinylidenefluoride based polymer prepared in aqueous emulsion polymerization usingnon-fluorinated non-ionic emulsifier as the principle emulsifier.Although the process of the invention has been generally illustratedwith respect to the polymerization of vinylidene fluoride basedpolymers, one of skill in the art will recognize that analogouspolymerization techniques can be applied to the preparation ofhomopolymers and copolymers of fluorinated monomers in general, and morespecific in VDF, TFE, and/or CTFE with co-reactive monomers fluorinatedor non-fluorinated such as hexafluoropropylene, perfluorovinyl ether,propane, vinyl acetate, and the like.

The predetermined amount of water, non-fluorinated surfactant, andoptionally chain transfer agent are placed in the reactor. Afterdegassing procedure, the reactor temperature is raised to the desiredpolymerization temperature, the predetermined amount of eithervinylidene fluoride alone or a mixture of monomers such as vinylidenefluoride and hexafluoropropylene are fed to the reactor. The temperatureof the reaction can vary depending on the characteristics of theinitiator used, but is typically from about 30° to 140° C., preferablyfrom about 50° to 130° C. Once the pressure in the reactor has reachedthe desired level, an initiator solution, made of either potassiumpersulfate, ammonium persulfate, or an emulsion of one or more organicperoxides such as propyl peroxidicarbonate, or dibutylperoxide in water,is charged to start the polymerization reaction. The polymerizationpressure may vary, but typically will be within the range of about 20 to50 atmospheres. Following the initiation of the reaction, the vinylidenefluoride or vinylidene/hexafluoropropylene mixture is continuously fedalong with additional initiator to maintain the desired pressure. Oncethe desired amount of polymer has been reached in the reactor, themonomer feed(s) will be stopped, but initiator feed is continued toconsume residual monomer(s). In order to avoid compositional drifts incase of copolymers, after reactor pressure drops to a given level, ashot of vinylidene fluoride is added to bring the vinylidene fluorideconcentration up. This step may be repeated more than one time dependingon the hexafluoropropylene concentration in the reactor. When thereactor pressure is low enough, about 300 psig, the initiator charge isstopped and after a delay time the reactor is cooled. The unreactedmonomer(s) are vented and the latex is recovered from the reactor. Thepolymer may then be isolated from the latex by standard methods, such asacid coagulation, freeze thaw or shear coagulation.

A paraffin antifoulant is an optional additive, and any long-chain,saturated, hydrocarbon wax or oil may be used for this purpose. Reactorloadings of the paraffin typically are from 0.01 percent to 0.3 percentby weight on the total monomer weight used.

A chain transfer agent may be added all at once at the beginning of thereaction, or it may be added in portions, or continuously throughout thecourse of the reaction. The amount of chain transfer agent added and itsmode of addition depends on the desired molecular weightcharacteristics, but is normally used in an amount of from about 0.5percent to about 5 percent based on total monomer weight used,preferably from about 0.5 percent to about 2 percent.

When copolymerization of vinylidene fluoride and hexafluoropropylene areperformed, or copolymerization of any two coreactive fluorinatedmonomers having differing reaction rates, the initial monomer chargeratio and the incremental monomer feed ratio during polymerization canbe adjusted according to apparent reactivity ratios to avoidcompositional drift in the final copolymer product.

The reaction can be started and maintained by the addition of anysuitable initiator known for the polymerization of fluorinated monomersincluding inorganic peroxides, “redox” combinations of oxidizing andreducing agents, and organic peroxides. Examples of typical inorganicperoxides are the ammonium or alkali metal salts of persulfates, whichhave useful activity in the 65° C. to 105° C. temperature range. “Redox”systems can operate at even lower temperatures and examples includecombinations of oxidants such as hydrogen peroxide, t-butylhydroperoxide, cumene hydroperoxide, or persulfate, and reductants suchas reduced metal salts, iron (II) salts being a particular example,optionally combined with activators such as sodium formaldehydesulfoxylate, metabisulfite, or ascorbic acid. Among the organicperoxides which can be used for the polymerization are the classes ofdialkyl peroxides, diacyl-peroxides, peroxyesters, andperoxydicarbonates. Exemplary of dialkyl peroxides is di-t-butylperoxide, of peroxyesters are t-butyl peroxypivalate and t-amylperoxypivalate, and of peroxydicarbonate, and di(n-propyl)peroxydicarbonate, diisopropyl peroxydicarbonate, di(sec-butyl)peroxydicarbonate, and di(2-ethylhexyl) peroxydicarbonate. The use ofdiisopropyl peroxydicarbonate for vinylidene fluoride polymerization andcopolymerization with other fluorinated monomers is taught in U.S. Pat.No. 3,475,396 and its use in making vinylidenefluoride/hexafluoropropylene copolymers is further illustrated in U.S.Pat. No. 4,360,652. The use of di(n-propyl) peroxydicarbonate invinylidene fluoride polymerizations is described in the PublishedUnexamined Application (Kokai) JP 58065711. The quantity of an initiatorrequired for a polymerization is related to its activity and thetemperature used for the polymerization. The total amount of initiatorused is generally between 0.05% to 2.5% by weight on the total monomerweight used. Typically, sufficient initiator is added at the beginningto start the reaction and then additional initiator may be optionallyadded to maintain the polymerization at a convenient rate. The initiatormay be added in pure form, in solution, in suspension, or in emulsion,depending upon the initiator chosen. As a particular example,peroxydicarbonates are conveniently added in the form of an aqueousemulsion.

While the invention is generally practiced with the PEG, PPG, and/orPTMG emulsifier as the sole emulsifiers, co-emulsifiers orco-surfactants could also be present in the invention, includingfluorinated or partially fluorinated or other non-fluorinatedemulsifiers.

The process of present invention is easy, convenient, cost effective,and more importantly is coagulum and adhesion free. The resultingpolymer dispersions have good latex stability and shelf-life, and a goodquality of film formation. Additionally, the particle size of dispersioncould be small (<100 nm) which in turn would be advantageous for manydirect applications of fluoropolymer in a latex form. Furthermore, thefluoropolymer produced with the process of this invention, has a higherpurity, with less extractable ions and less low molecular weightpolymers.

The following examples further illustrate the best mode contemplated bythe inventors for the practice of their invention and should beconsidered as illustrative and not in limitation thereof.

EXAMPLES

The glycol-based emulsifiers used in this example include polyethyleneglycol acrylate (PEGA), polyethylene glycol (PEG), and polyethyleneglycol octyl-phenyl ether (Triton X-100), polypropylene glycol acrylate(PPGA), polypropylene glycol (PPG), polyethylene glycol methacrylate(PEG-MA), dimethyl polyethylene glycol (DMPEG), polyethylene glycolbutyl ether (PEGBE), polypropylene glycol methacrylate (PPG-MA),polypropylene glycol di-methacrylate (PPG-DMA), and polytetramethyleneglycol (PTMG). Inspection of results in the following table indicatesthat a with a low loading of the emulsifiers, emulsions offluoropolymers having particle sizes of approximately 100 nm and higherwere produced. The solid level of these novel emulsions were as high as42%.

To a 1.7 liter agitated-autoclave reactor was added one liter ofDI-water along with the reported amount of 10% aqueous solution ofemulsifier (as shown in Table 1). The mixture was purged with argon andthen heated to desired temperature of 82° C. The reactor was thencharged with VF2/HFP to reach pressure of 4510 kPa. A continuous feed ofthe 1% aqueous initiator solution was added to the reaction and thepressure was maintained at 4480 kPa by adding as needed VF2/HFP. Afterthe pre-determined amount of VF2 in the reactor was reached, addition ofmonomers were stopped and only initiator addition of initiator wascontinued till the pressure in the reactor was dropped to 300 psi. Aftercooling to room temperature, the reactor was emptied. Gravimetric solidsand particle size measurements of the latex were conducted.

To a 7.8 liter agitated-autoclave reactor was added 3.4 liter ofDI-water, 1 g paraffin wax along with the predetermined amount ofemulsifier either in neat form or in 10% aqueous solution (as shown inTable 2). The mixture was purged with argon and then heated to 83° C.The reactor was then charged with VF2/HFP to reach pressure of 4510 kPa.A continuous feed of the 1% aqueous initiator solution was added to thereaction and the pressure was maintained at 4480 kPa by adding as neededVF2/HFP. After the pre-determined amount of VF2 in the reactor wasreached, addition of monomers and initiator were stopped but reactioncontinued till the pressure in the reactor was dropped to 300 psi. Aftercooling to room temperature, the reactor was emptied. Gravimetric solidsand particle size measurements of the latex were conducted. The latexstability was assessed based on settling characteristics; for example,latexes with particle size less than 150 nm did not settled even after300 days of storage at ambient condition and latexes with particle sizelarger than 150 nm did not settled before 100 days. The particle size ofdispersion was determined using a Nicomp Model 380 Sub-Micron ParticleSizer including single mode 35 mW Laser diode with wavelength of 639 nm.

TABLE 1 Particle Surfactant surfactant Initiator⁽¹⁾ VDF⁽²⁾ Solids sizetype solution, g ml Ml HFP⁽³⁾ % (nm) PEGA 7.5 186 473 193 37 108 PEGA7.5 154 449 114 29 116 PEGA 4 100 541 160 37 143 X-100 7.5 195 453 20235 79 PEG 7.6 64 451 194 35 232 (200) PEG 7.5 109 450 191 36 235 (300)PEG 7.5 122 360 217 42 — PEG 7.5 127 450 200 35 215 (570) PPG 7.5 123450 198 36 — (450) PPGA 7.5 141 449 212 36 100 PPGA 3 99 450 202 35 150PPGA 5.11 78 450 106 33 122 PPGA 5 59 500 102 32 123 PPGA 5 58 549 0 27— PPGA 6 81 650 0 32 — ⁽¹⁾Initiator solution was made of 1% potassiumpersulfate and 1% sodium acetate ⁽²⁾Density of VDF at the feedingcondition is 0.83 g/ml ⁽³⁾Density of VDF at the feeding condition is1.35 g/ml

TABLE 2 Surfactant VF2 KPS⁽¹⁾ Surfactant Particle Type (g) HFP (g) (ml)(g) Solids % Size (nm) PPG 1906 258 280 2.0 34 202 PEGMA 1906 872 4762.0 38 134 PPGMA 1904 872 339 2.0 40 125 PPGMA 1908 846 519 3.0 38 112DMPEG 1902 834 355 2.0 39 206 DMPEG 1908 880 640 3.0 38 207 PEGBE 1906858 370 1.5 41 221 PPGDMA 2006 914 203 2.0 45 214 PPGDMA 2018 898 2394.0 44 207 PTMG 2016 892 233 2.0 42 251 PTMG 2018 898 239 4.0 44 260⁽¹⁾Initiator solution was made of 1% potassium persulfate and 1% sodiumacetate

1. An aqueous stable thermoplastic fluoropolymer dispersion comprising:a) a fluoropolymer containing from 70 to 100 mole percent of vinylidenefluoride monomer units, and containing residues of one or more ammoniumor alkali metal salts of persulfates; and b) as the only surfactant from100 ppm to 2 percent, based on the weight of the fluoropolymer solids,of total emulsifier(s) consisting of nonionic emulsifiers consisting ofpolyethylene glycol, polypropylene glycol and/or polytetramethyleneglycol (PTMG) segments with repeating units of from 2 to 100, whereinsaid fluoropolymer is in the form of particles having an averageparticle size from 50 to 500 nm and said fluoropolymer dispersion has asolid content of 15 to 70 weight percent, and wherein said fluoropolymerdispersion is free of fluorinated-surfactant.
 2. The fluoropolymerdispersion of claim 1, wherein said fluoropolymer dispersion has a solidcontent of from 20 to 65 weight percent.
 3. The fluoropolymer dispersionof claim 1, wherein said fluoropolymer particles have an averageparticle size of 100 to 350 nm.
 4. The fluoropolymer composition ofclaim 1 comprising from 100 ppm to 1 percent, based on the weight of thefluoropolymer solids, of one or more emulsifiers having polyethyleneglycol, polypropylene glycol, and/or polytetramethylene glycol segments.5. The fluoropolymer composition of claim 1 comprising from 100 ppm to ½percent, based on the weight of the fluoropolymer solids, of one or moreemulsifiers having polyethylene glycol, polypropylene glycol, and/orpolytetramethylene glycol segments.
 6. The fluoropolymer composition ofclaim 1 wherein said emulsifier having polyethylene glycol,polypropylene glycol segments, and/or polytetramethylene glycol isselected from the group consisting of polyethylene glycol acrylate,polyethylene glycol, polyethylene glycol phenol oxide, polypropyleneglycol acrylate, polypropylene glycol, polyethylene glycol methacrylate,dimethyl polyethylene glycol, polyethylene glycol butyl ether,polypropylene glycol methacrylate, polypropylene glycol di-methacrylate,polytetramethylene glycol and mixtures thereof.
 7. The fluoropolymercomposition of claim 1 wherein said emulsifier(s) have polyethyleneglycol, polypropylene glycol, and/or polytetramethylene glycol segmentswith repeating units of from 3 to 100.